Hydrofluoric acid is a solution of hydrogen fluoride in water. Together with hydrogen fluoride, hydrofluoric acid is a valued source of fluorine, being the precursor to numerous pharmaceuticals, diverse polymers (e.g. Teflon), and most other synthetic materials that contain fluorine. Hydrofluoric acid is best known to the public for its ability to dissolve glass by reacting with SiO2, the major component of most glasses. This dissolution process can be described as follows:
SiO
2(s) + 4HF
(aq) 
SiF
4(g) + 2H
2O
(l) SiO
2(s) + 6HF
(aq) H
2[SiF
6]
(aq) + 2H
2O
(l) Solutions of less than 20% HF can produce pain and redness with delay up to 24 hours after skin exposure. 20 to 50% HF produces pain and redness within 8 hours, and solutions of more than 50% produce immediate burning, redness and blister formation. Contact of the skin with the anhydrous liquid produces severe burns
A case of fluoride poisoning of a girl aged 2(1/2) years is reported. "Although the possibility of ingestion was originally denied by the mother, repeated questioning revealed that prior to becoming ill the child had been playing with a laundry powder. The mother had obtained this material from a commercial laundry. The powder was identified as "Bayline Brand Laundry Sour" (manufactured by BASF Wyandotte, Michigan), a whitener sold only to commercial laundries. This contained sodium silicofluoride (Na2SiF6) as its major ingredient ..."
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